The Thanksgiving Evening Fog Battle - I Lost!

  Thanksgiving day was unseasonably mild. We started off with cloudy skies and light fog in the air but by afternoon skies started to clear and Indianapolis had its first sunshine in six days. It was still clear at sunset but there was a mist in the air. Persistent cloud cover all these days hadn't given the ground a chance to dry out from heavy rain earlier in the week, and as skies cleared and temperatures dropped, light fog started to form. Still, since this was the first clear night in a long time, I decided to try to get out and observe. It turned out to be a battle with fog, and fog won. 

  My target tonight was the Eclipsing Binary star SS Ceti. I get on "EB (eclipsing binary) kicks" every now and then. These are double stars in close orbits with one another, and the plane of the orbit lies in our line of sight, which means that from Earth one star often passes in front of or behind the other star. These stars lie too close together to be seen as two separate stars in a telescope. However, what we can see is that the brighter star drops in brightness and then brightens back up again, usually in a matter of hours, as the dimmer star eclipses or passes in front of it. SS Ceti does a five hour dimming-and-brightening every three days (2.973976 days to be exact) and it was predicted to eclipse at 12:30 AM Friday morning our time. The star was expected to start getting dim around 10:00 PM Thursday night. 

  I almost called off observing to begin with because of the light fog in the air, but skies were clear so I hauled out the telescope and started observing. Even though it was very starry above my head, the horizons seemed to be lit up by the low-lying fog. The temperature was about 40 degrees F and the humidity was something like 90%. I guess I knew this would be a losing battle, but I was hoping there was enough of a steady light breeze to keep the telescope's corrector lens and my eyepieces from fogging up too much. 

  It was going well at first. I saw SS Ceti drop from 10.6 magnitude at 10:34 PM to 10.9 magnitude by 11:08 PM. It took a big drop from there to 11.2 magnitude by 11:06 PM. I jotted down my estimates and times, but dew was already forming all over the dew cap and tube. The finder scope was also fogging up. The mist suspended in the air was starting to make my clear sky with all of those blazing winter stars start to look murky, and I had the sinking feeling that I wasn't going to be able to do much more observing. By 11:45 PM. SS Ceti was getting hard to see because it was so faint, but even the easy-to-see stars around it were starting to look dim. I looked into the front of the telescope and it was clear that the big lens was starting to fog up. I had to give up on watching the rest of the SS Ceti eclipse.

  I wanted to make one useful observation tonight, so I went back inside and grabbed my chart for UX Orionis, since this star has been very active all month. However, by the time I was back outside the optics on the telescope had reached the saturation point. The front lens was totally fogged over and nothing could be seen through the scope at all. I had to admit defeat and call it a night without making one useful variable star estimate worth reporting to the AAVSO. I couldn't even really report the estimates I made of SS Ceti as it fell in brightness, because what's really valuable about an eclipsing binary star is an estimated time of minimum brightness, and I couldn't get that without catching it on the recovery after 12:30 AM. 

  You can't win 'em all. I can observe under a lot of bad conditions, but 90% humidity isn't one of them. All I could do was hope for better conditions the next night. There will be other chances to observe SS Ceti or some other EB star, and YSO stars like UX Orionis.